London's Heathrow Airport is "fully operational" and returning to normal after an emergency landing Friday forced the closing of both runways, the airport said-- but many travelers are likely to suffer delays anyway.

British Airways has canceled all its inbound and outbound short-haul flights until 4 p.m. (11 a.m. ET) as a result of the incident.

And Heathrow Airport has warned of disruption to travel that could last all day.

So far, 23 planes have been diverted to other airports and 19 flights canceled, some arrivals and some departures, a spokeswoman said Friday morning.

The airport is working to return to normal service as soon as possible, she said, but passengers are advised to check with their airlines.

A British Airways plane bound for Oslo was forced to make the emergency landing "due to a technical fault," the airline said.

Flight BA762 turned back less than half an hour after taking off for the Norwegian capital, it said.

The Airbus A319 aircraft was carrying 75 passengers and five crew members, the airline said. The passengers were evacuated from the plane on emergency slides.

"Airline colleagues are now caring for customers in the airport terminal," said British Airways.

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London Ambulance Service treated three patients for minor injuries after the emergency landing, it said on Twitter.

British Airways said it would be carrying out a full investigation into the incident, alongside the Air Accident Investigation Branch, part of the UK Department for Transport.

The slides were deployed on the left side of the aircraft, indicating that the problem was with the right engine, said CNN's Richard Quest.

Planes can fly safely even if only one engine is operational, he said.

London Fire Brigade said one of its crews helped the airport fire service put out an aircraft fire. "We believe the fire is now out," it said via Twitter.

Heathrow, which is a major international hub, was ranked the third busiest airport in the world in 2012 after Atlanta and Beijing, according to Airports Council International.

Monday is a holiday in the United Kingdom, so many people will be taking flights Friday to take advantage of the long weekend.

Holidaymaker Aileen Wilson was one of many travelers whose flight was grounded by the incident.

"We've just been sitting, waiting in a plane meant to take off" this morning, she told CNN iReport. "At first we were told ongoing incident and then emergency landing. We (are) still waiting to take off (and) not allowed out of plane!"

Instagram user Shazia Shaikh took a photograph from the office where she works at Heathrow Airport of emergency vehicles surrounding a plane.